Bone remodeling is the dynamic process by which tissue mass and skeletal architecture are maintained. The process is a balance between bone resorption and bone formation, with two cell types, the osteoclast and osteoblast, thought to be the major players. Osteoblasts synthesize and deposit new bone into cavities that are excavated by osteoclasts. The activities of osteoblasts and osteoclasts are regulated by many factors, systemic and local, including growth factors.
Many of the proteins that influence the proliferation, differentiation, and activity of osteoblasts, osteoclasts, and their precursors also affect these processes in chondrocytes, the cells responsible for cartilage formation (chondrogenesis). These proteins include platelet-derived growth factor (PDGF), insulin-like growth factor (IGF), basic fibroblast growth factor (bFGF), transforming growth factor beta (TGF-xcex2), bone morphogenetic proteins (BMP), and cartilage-derived growth factor (CDGF).
The exact mode by which PDGF affects the growth of osteoblasts is not yet clearly understood, however, this growth factor is generally believed to play a key role in the regulation of both normal skeletal remodeling and fracture repair. Biologically active PDGF is found as a homodimer or a heterodimer of the component A and B chains. In vitro studies have shown PDGF to be mitogenic for osteoblasts (Abdennagy et al., Cell Biol. Internat. Rep. 16(3):235-247, 1992). Mitogenic activity as well as chemotactic activities associated with PDGF have been demonstrated when the growth factor is added to normal osteoblast-like cells (Tuskamota et al. Biochem. Biophys. Res. Comm., 175(3):745-747, 1991) and primary osteoblast cultures (Centrella et al. Endocrinol. 125 (1):13-19, 1989). Recent studies have demonstrated that the osteoblast produces the AA isoform of PDGF (Zhang et al., Am. J. Physiol. 261: c348-c354, 1991).
PDGF has been shown to be useful for promoting the repair of both soft and hard tissues. For example, PDGF has been shown to promote the regeneration of bone and ligament in patients suffering from periodontal disease (Howell et al., J. Periodontol. 68:1186-1193, 1997). As disclosed in U.S. Pat. No. 5,533,836, PDGF stimulates the growth of osteoblasts, and this activity is enhanced in the presence of vitamin D. PDGF has also been shown to promote the healing of gastrointestinal ulcers (U.S. Pat. No. 5,234,908) and dermal ulcers (Robson et al., Lancet 339:23-25, 1992; Steed et al., J. Vasc. Surg. 21:71-81, 1995). The use of PDGF for stimulating chondrocyte proliferation and regenerating cartilage is disclosed in U.S. Pat. No. 6,001,352.
A PDGF homolog known as xe2x80x9czvegf3xe2x80x9d was recently identified (U.S. patent application Ser. No. 09/457,066). This protein has also been designated xe2x80x9cVEGF-Rxe2x80x9d (WIPO Publication WO 99/37671). A related protein, designated xe2x80x9czvegf4xe2x80x9d, has also been identified (U.S. patent applications Ser. Nos. 09/304,216 and 60/132,250). Zvegf3 and zvegf4 are multi-domain proteins with significant homology to the PDGF/VEGF family of growth factors. WO 99/37671 discloses that VEGF-R is an angiogenic factor.
Despite the increasing knowledge of the role of growth factors in tissue growth and repair, there remains a need in the art for materials and methods for promoting the growth of bone, ligament, and cartilage. There also remains a need the art for materials and methods for modulating the proliferation and differentiation of cells in vitro and in vivo.
The present invention provides a method for promoting growth of bone, ligament, or cartilage in a mammal comprising administering to said mammal a composition comprising a pharmacologically effective amount of zvegf4 in combination with a pharmaceutically acceptable delivery vehicle. Within certain embodiments of the invention the delivery vehicle is powdered bone, tricalcium phosphate, hydroxyapatite, polymethacrylate, a biodegradable polyester, an aqueous polymeric gel, or a fibrin sealant. Within another embodiment of the invention the composition is locally administered at a site of a bony defect, such as a fracture, bone graft site, implant site, or periodontal pocket. Within another embodiment of the. invention, the composition is administered systemically. Within a further embodiment of the invention, the zvegf4 is covalently linked to a bone-targetting agent. Within a further embodiment of the invention, the composition is locally administered at a joint. The composition may further comprise a protein selected from the group consisting of insulin-like growth factor 1, platelet-derived growth factor, epidermal growth factor, transforming growth factor-alpha, transforming growth factor-beta, a bone morphogenetic protein, parathyroid hormone, osteoprotegerin, or a fibroblast growth factor.
The invention also provides a method for promoting proliferation or differentiation of cells comprising culturing the cells in an effective amount of zvegf4, wherein the cells are osteoblasts, osteoclasts, chondrocytes, or bone marrow stem cells. Within one embodiment the cells are bone marrow stem cells, and the method comprises harvesting the bone marrow stem cells from a patient prior to culturing. Within other embodiments the method further comprises the step of recovering osteoblasts, osteoclasts, or chrodrocytes from the cultured cells.
The invention also provides a method for promoting cartilage growth comprising the steps of (a) culturing chondrocytes ex vivo in the presence of zvegf4 under conditions wherein the chondrocytes proliferate, and and (b) placing the cultured chondrocytes into a mammal where cartilage is to be grown. Within one embodiment the chondrocytes are placed into the mammal in association with a biodegradable matrix having sufficient porosity to permit cell ingrowth. Within a related embodiment the matrix comprises a protein selected from the group consisting of zvegf4, insulin-like growth factor 1, platelet-derived growth factor, epidermal growth factor, transforming growth factor-alpha, transforming growth factor-beta, a bone morphogenetic protein, parathyroid hormone, or a fibroblast growth factor.
These and other aspects of the invention will become evident upon reference to the following detailed disclosure and the accompanying drawing. FIGS. 1A-1G are a Hopp/Woods hydrophilicity profile of the amino acid sequence shown in SEQ ID NO:2. The profile is based on a sliding six-residue window. Buried G, S, and T residues and exposed H, Y, and W residues were ignored. These residues are indicated in the figure by lower case letters.
As used herein, the term xe2x80x9cbony defectxe2x80x9d denotes a defect or void in a bone where restoration of the bone is desirable. Bony defects may arise from injury, surgery, tumor removal, ulceration, infection, or other causes, and include congenital defects. Examples of bony defects include fractures, voids resulting from tumor removal, and bone loss resulting from periodontal disease.
The terms xe2x80x9clocally administeredxe2x80x9d and xe2x80x9clocal administrationxe2x80x9d are used to describe the application of a pharmaceutical agent at the intended site of action. Examples of local administration include, without limitation, injection into a joint space, implantation of a solid or semi-solid matrix, and direct application at a surgical site or wound. Local administration does not preclude the transmission of minor amounts of the agent to other parts of the body, such as by diffusion or circulation.
The term xe2x80x9czvegf4 proteinxe2x80x9d is used herein to denote proteins comprising a biologically active portion of a zvegf4 polypeptide (e.g., human zvegf4 as shown in SEQ ID NO:2 or mouse zvegf4 as shown in SEQ ID NO:4) that is mitogenic or chemotactic for mesenchymal cells. Experimental evidence indicates that biologically active zvegf4 is a dimeric protein. Zvegf4 proteins include homodimers and heterodimers as disclosed below. Using methods known in the art, zvegf4 proteins can be prepared in a variety of forms, including glycosylated or non-glycosylated; pegylated or non-pegylated; with or without an initial methionine residues; and as fusion proteins as disclosed in more detail below.
The present invention provides methods for promoting the growth of bone, connective tissue (including ligament, tendon, and cartilage), and related cell types using zvegf4 proteins. Zvegf4 is a protein that is structurally related to platelet-derived growth factor (PDGF) and the vascular endothelial growth factors (VEGF). The zvegf4 polypeptide chain comprises a growth factor domain and a CUB domain. The growth factor domain is characterized by an arrangement of cysteine residues and beta strands that is characteristic of the xe2x80x9ccystine knotxe2x80x9d structure of the PDGF family. The CUB domain shows sequence homology to CUB domains in the neuropilins (Takagi et al., Neuron 7:295-307, 1991; Soker et al., ibid.), human bone morphogenetic protein-1 (Wozney et al., Science 242:1528-1534, 1988), porcine seminal plasma protein and bovine acidic seminal fluid protein (Romero et al., Nat. Struct. Biol. 4:783-788, 1997), and X. laevis tolloid-like protein (Lin et al., Dev. Growth Differ. 39:43-51, 1997).
Structural predictions based on the zvegf4 sequence and its homology to other growth factors suggests that the polypeptide can form homomultimers or heteromultimers having growth factor activity, i.e., modulating one or more of cell proliferation, migration, differentiation, and metabolism. While not wishing to be bound by theory, the similarity of zvegf4 to other members of the PDGF/VEGF family suggests that zvegf4 may also form heteromultimers with other members of the family, including VEGF, VEGF-B, VEGF-C, VEGF-D, zvegf3 (SEQ ID NO:5), PIGF (Maglione et al., Proc. Natl. Acad. Sci. USA 88:9267-9271, 1991), PDGF-A (Murray et al., U.S. Pat. No. 4,899,919; Heldin et al., U.S. Pat. No. 5,219,759), or PDGF-B (Chiu et al., Cell 37:123-129, 1984; Johnsson et al., EMBO J. 3:921-928, 1984).
A representative human zvegf4 polypeptide sequence is shown in SEQ ID NO:2, and a representative mouse zvegf4 polypeptide sequence is shown in SEQ ID NO:4. DNAs encoding these polypeptides are shown in SEQ ID NOS: 1 and 3, respectively. Analysis of the amino acid sequence shown in SEQ ID NO:2 indicates that residues 1 to 18 form a secretory peptide. The CUB domain extends from residue 52 to residue 179. A propeptide-like sequence extends from residue 180 to residue 257, and includes two potential cleavage sites at its carboxyl terminus, a dibasic site at residues 254-255 and a target site for furin or a furin-like protease at residues 254-257. The growth factor domain extends from residue 258 to residue 370. Those skilled in the art will recognize that domain boundaries are somewhat imprecise and can be expected to vary by up to xc2x15 residues from the specified positions. Processing of recombinant zvegf4 produced in a baculovirus expression system has been found to occur between residues 249 and 250. Signal peptide cleavage is predicted to occur after residue 18 (xc2x13 residues), and cleavage after residue 34 has been observed in protein from the baculovirus system. This analysis suggests that the zvegf4 polypeptide chain may be cleaved to produce a plurality of monomeric species as shown in Table 1.
Zvegf4 can thus be prepared in a variety of multimeric forms comprising a zvegf4 polypeptide as disclosed above. Variants and derivatives of these polypeptides can also be prepared as disclosed herein.
Zvegf4 proteins can be prepared as fusion proteins comprising amino- or carboxyl-terminal extensions, such as an amino-terminal methionine residue, an affinity tag, or a targetting polypeptide. For example, a zvegf4 protein can be prepared as a fusion with an affinity tag to facilitate purification. In principal, any peptide or protein for which an antibody or other specific binding agent is available can be used as an affinity tag. Affinity tags include, for example, a poly-histidine tract, protein A (Nilsson et al., EMBO J. 4:1075, 1985; Nilsson et al., Methods Enzymol. 198:3, 1991), glutathione S transferase (Smith and Johnson, Gene 67:31, 1988), Glu-Glu affinity tag (Grussenmeyer et al., Proc. Natl. Acad. Sci. USA 82:7952-4, 1985), substance P, Flag(trademark) peptide (Hopp et al., Biotechnology 6:1204-1210, 1988), streptavidin binding peptide, maltose binding protein (Guan et al., Gene 67:21-30, 1987), cellulose binding protein, thioredoxin, ubiquitin, T7 polymerase, or other antigenic epitope or binding domain. Fusion of zvegf4 to, for example, maltose binding protein or glutatione S transferase, can be used to improve yield in bacterial expression systems. In these instances the non-zvegf4 portion of the fusion protein ordinarily will be removed prior to use. Separation of the zvegf4 and non-zvegf4 portions of the fusion protein is facilitated by providing a specific cleavage site between the two portions. Such methods are well known in the art. Zvegf4 can also be fused to a targetting peptide, such as an antibody (including polyclonal antibodies, monoclonal antibodies, antigen-binding fragments thereof such as F(abxe2x80x2)2 and Fab fragments, single chain antibodies, and the like), calcitonin, or other peptidic moiety that binds to bone or connective tissue.
Variations can be made in the zvegf4 amino acid sequences shown in SEQ ID NO:2 and SEQ ID NO:4. Such variations include amino acid substitutions, deletions, and insertions. Amino acid sequence changes are made in zvegf4 polypeptides so as to minimize disruption of higher order structure essential to biological activity. In general, conservative amino acid changes are preferred. Changes in amino acid residues will be made so as not to disrupt the cystine knot and xe2x80x9cbow tiexe2x80x9d arrangement of loops in the growth factor domain that is characteristic of the protein family. Conserved motifs will also be maintained. The effects of amino acid sequence changes can be predicted by computer modeling as disclosed above or determined by analysis of crystal structure (see, e.g., Lapthorn et al., Nature 369:455, 1994). A hydrophobicity profile of SEQ ID NO:2 is shown in FIGS. 1A-1G. Those skilled in the art will recognize that this hydrophobicity will be taken into account when designing alterations in the amino acid sequence of a zvegf4 polypeptide, so as not to disrupt the overall profile. Additional guidance in selecting amino acid subsitutions is provided by a comparison of the mouse (SEQ ID NO:4) and human (SEQ ID NO:2) zvegf4 sequences. The amino acid sequence is highly conserved between mouse and human zvegf4s, with an overall amino acid sequence identity of 85.1%.
It is preferred that the sequence of a zvegf4 polypeptide be at least 95% identical to the corresponding region of SEQ ID NO:2 or SEQ ID NO:4. Percent sequence identity is determined by conventional methods. See, for example, Altschul et al., Bull. Math. Bio. 48:603-616, 1986, and Henikoff and Henikoff, Proc. Natl. Acad. Sci. USA 89:10915-10919, 1992. Briefly, two amino acid sequences are aligned to optimize the alignment scores using a gap opening penalty of 10, a gap extension penalty of 1, and the xe2x80x9cBLOSUM62xe2x80x9d scoring matrix of Henikoff and Henikoff (ibid.). The percent identity is then calculated as:             "AutoLeftMatch"              Total        ⁢                  xe2x80x83                ⁢        number        ⁢                              xe2x80x83                    ⁢                      xe2x80x83                          ⁢        of        ⁢                  xe2x80x83                ⁢        identical        ⁢                  xe2x80x83                ⁢        matches            "AutoRightMatch"                   [length of the longer sequence plus the
   number of gaps introduced into the longer
sequence in order to align the two sequences]        xc3x97  100
Zvegf4 proteins can also comprise non-naturally occurring amino acid residues. Non-naturally occurring amino acids include, without limitation, trans-3-methylproline, 2,4-methanoproline, cis-4-hydroxyproline, trans4-hydroxyproline, N-methylglycine, allo-threonine, methylthreonine, hydroxyethylcysteine, hydroxyethylhomocysteine, nitroglutamine, homoglutamine, pipecolic acid, tert-leucine, norvaline, 2-azaphenylalanine, 3-azaphenylalanine, 4-azaphenylalanine, and 4-fluorophenylalanine. Several methods are known in the art for incorporating non-naturally occurring amino acid residues into proteins. For example, an in vitro system can be employed wherein nonsense mutations are suppressed using chemically aminoacylated suppressor tRNAs. Methods for synthesizing amino acids and aminoacylating tRNA are known in the art. Transcription and translation of plasmids containing nonsense mutations is carried out in a cell-free system comprising an E. coli S30 extract and commercially available enzymes and other reagents. Proteins are purified by chromatography. See, for example, Robertson et al., J. Am. Chem. Soc. 113:2722, 1991; Ellman et al., Methods Enzymol. 202:301, 1991; Chung et al., Science 259:806-809, 1993; and Chung et al., Proc. Natl. Acad. Sci. USA 90:10145-10149, 1993). In a second method, translation is carried out in Xenopus oocytes by microinjection of mutated mRNA and chemically aminoacylated suppressor tRNAs (Turcatti et al., J. Biol. Chem. 271:19991-19998, 1996). Within a third method, E. coli cells are cultured in the absence of a natural amino acid that is to be replaced (e.g., phenylalanine) and in the presence of the desired non-naturally occurring amino acid(s) (e.g., 2-azaphenylalanine, 3-azaphenylalanine, 4-azaphenylalanine, or 4-fluorophenylalanine). The non-naturally occurring amino acid is incorporated into the protein in place of its natural counterpart. See, Koide et al., Biochem. 33:7470-7476, 1994. Naturally occurring amino acid residues can be converted to non-naturally occurring species by in vitro chemical modification. Chemical modification can be combined with site-directed mutagenesis to further expand the range of substitutions (Wynn and Richards, Protein Sci. 2:395-403, 1993).
Essential amino acids in zvegf4 proteins can be identified according to procedures known in the art, such as site-directed mutagenesis or alanine-scanning mutagenesis (Cunningham and Wells, Science 244, 1081-1085, 1989; Bass et al., Proc. Natl. Acad. Sci. USA 88:4498-4502, 1991). Multiple amino acid substitutions can be made and tested using known methods of mutagenesis and screening, such as those disclosed by Reidhaar-Olson and Sauer (Science 241:53-57, 1988) or Bowie and Sauer (Proc. Natl. Acad. Sci. USA 86:2152-2156, 1989). Other methods that can be used include phage display (e.g., Lowman et al., Biochem. 30:10832-10837, 1991; Ladner et al., U.S. Pat. No. 5,223,409; Huse, WIPO Publication WO 92/06204), region-directed mutagenesis (Derbyshire et al., Gene 46:145, 1986; Ner et al., DNA 7:127, 1988), and DNA shuffling as disclosed by Stemmer (Nature 370:389-391, 1994) and Stemmer (Proc. Natl. Acad. Sci. USA 91:10747-10751, 1994). The resultant mutant molecules are tested for mitogenic activity or other properties (e.g., receptor binding) to identify amino acid residues that are critical to the activity of the molecule. Mutagenesis can be combined with high volume or high-throughput screening methods to detect biological activity of zvegf4 variant polypeptides, in particular biological activity in modulating cell proliferation or cell differentiation. For example, mitogenesis assays that measure dye incorporation or 3H-thymidine incorporation can be carried out on large numbers of samples.
Using the methods discussed above, one of ordinary skill in the art can identify and/or prepare a variety of polypeptides that are homologous to the zvegf4 polypeptides disclosed above in Table 1 and retain the biological properties of the wild-type protein.
Zvegf4 proteins for use within the present invention, including full-length polypeptides, biologically active fragments, and fusion proteins, can be produced in genetically engineered host cells according to conventional techniques. Suitable host cells are those cell types that can be transformed or transfected with exogenous DNA and grown in culture, and include bacteria, fungal cells, and cultured higher eukaryotic cells (including cultured cells of multicellular organisms). Techniques for manipulating cloned DNA molecules and introducing exogenous DNA into a variety of host cells are disclosed by Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989, and Ausubel et al., eds., Current Protocols in Molecular Biology, Green and Wiley and Sons, NY., 1993.
In general, a DNA sequence encoding a zvegf4 polypeptide is operably linked to other genetic elements required for its expression, generally including a transcription promoter and terminator, within an expression vector. The vector will also commonly contain one or more selectable markers and one or more origins of replication, although those skilled in the art will recognize that within certain systems selectable markers may be provided on separate vectors, and replication of the exogenous DNA may be provided by integration into the host cell genome. Selection of promoters, terminators, selectable markers, vectors and other elements is a matter of routine design within the level of ordinary skill in the art. Many such elements are described in the literature and are available through commercial suppliers.
To direct a zvegf4 polypeptide into the secretory pathway of a host cell, a secretory signal sequence (also known as a leader sequence, prepro sequence or pre sequence) is provided in the expression vector. The secretory signal sequence may be that of zvegf4, or may be derived from another secreted protein (e.g., t-PA; see, U.S. Pat. No. 5,641,655) or synthesized de novo. The secretory signal sequence is operably linked to the zvegf4 DNA sequence, i.e., the two sequences are joined in the correct reading frame and positioned to direct the newly synthesized polypeptide into the secretory pathway of the host cell. Secretory signal sequences are commonly positioned 5xe2x80x2 to the DNA sequence encoding the polypeptide of interest, although certain signal sequences may be positioned elsewhere in the DNA sequence of interest (see, e.g., Welch et al., U.S. Pat. No. 5,037,743; Holland et al., U.S. Pat. No. 5,143,830).
Expression of zvegf4 polypeptides via a host cell secretory pathway is expected to result in the production of multimeric proteins. As noted above, such multimers include both homomultimers and heteromultimers, the latter including proteins comprising only zvegf4 polypeptides and proteins including zvegf4 and heterologous polypeptides. For example, a heteromultimer comprising a zvegf4 polypeptide and a polypeptide from a related family member (e.g., VEGF, VEGF-B, VEGF-C, VEGF-D, zvegf3, PIGF, PDGF-A, or PDGF-B) can be produced by co-expression of the two polypeptides in a host cell. Sequences encoding these other family members are known. See, for example, Dvorak et al, ibid.; Olofsson et al, ibid.; Hayward et al., ibid.; Joukov et al., ibid.; Oliviero et al., ibid.; Achen et al., ibid.; Maglione et al., ibid.; Heldin et al., U.S. Pat. No. 5,219,759; and Johnsson et al., ibid. If a mixture of proteins results from expression, individual species are isolated by conventional methods. Monomers, dimers, and higher order multimers are separated by, for example, size exclusion chromatography. Heteromultimers can be separated from homomultimers by immunoaffinity chromatography using antibodies specific for individual dimers or by sequential immunoaffinity steps using antibodies specific for individual component polypeptides. See, in general, U.S. Pat. No. 5,094,941. Multimers may also be assembled in vitro upon incubation of component polypeptides under suitable conditions. In general, in vitro assembly will include incubating the protein mixture under denaturing and reducing conditions followed by refolding and reoxidation of the polypeptides to from homodimers and heterodimers. Recovery and assembly of proteins expressed in bacterial cells is disclosed below.
Zvegf4 proteins can be produced in eukaryotic host cells, including fungal cells (e.g., Saccharomyces cerevisiae, Pichia methanolica, and Pichia pastoris), mammalian cells, plant cells, and insect cells according to conventional methods. See, for example, Kawasaki, U.S. Pat. No. 4,599,311; Kawasaki et al., U.S. Pat. No. 4,931,373; Brake, U.S. Pat. No. 4,870,008; Welch et al., U.S. Pat. No. 5,037,743; Murray et al., U.S. Pat. No. 4,845,075; Gleeson et al., J. Gen. Microbiol. 132:3459-3465, 1986; Cregg, U.S. Pat. No. 4,882,279; Raymond et al., Yeast 14:11-23, 1998; McKnight et al., U.S. Pat. No. 4,935,349; Sumino et al., U.S. Pat. No. 5,162,228; Lambowitz, U.S. Pat. No. 4,486,533; Raymond et al., 5,854,039; Raymond, U.S. Pat. Nos. 5,716,808, 5,736,383, and 5,888,768; Levinson et al., U.S. Pat. No. 4,713,339; Hagen et al., U.S. Pat. No. 4,784,950; Palmiter et al., U.S. Pat. No. 4,579,821; Foster et al., U.S. Pat. No. 4,959,318; Mulvihill et al., U.S. Pat. No. 5,648,254; Moore et al., U.S. Pat. No. 5,622,839; Kuestner et al., U.S. Pat. No. 6,008,322; Sinkar et al., J Biosci. (Bangalore) 11:47-58, 1987; Luckow et al., J. Virol. 67:4566-4579, 1993; Hill-Perkins and Possee, J. Gen. Virol. 71:971-976, 1990; Bonning et al., J. Gen. Virol. 75:1551-1556, 1994; and Chazenbalk and Rapoport, J. Biol. Chem. 270:1543-1549, 1995. Suitable host strain and cell lines are known in the art and available from public depositories such as the American Type Culture Collection, Manassas, Va., USA. Suitable cultured mammalian cells include the COS-1 (ATCC No. CRL 1650), COS-7 (ATCC No. CRL 1651), BHK (ATCC No. CRL 1632), BHK 570 (ATCC No. CRL 10314), 293 (ATCC No. CRL 1573; Graham et al., J. Gen. Virol. 36:59-72, 1977) and Chinese hamster ovary (e.g. CHO-K1; ATCC No. CCL 61) cell lines. Expression vectors for use in mammalian cells include pZP-1 and pZP-9, which have been deposited with the American Type Culture Collection, Manassas, Va., USA under accession numbers 98669 and 98668, respectively. Cells, expression vectors, expression kits, and other materials are available from commercial suppliers.
Prokaryotic host cells, including strains of the bacteria Escherichia coli, Bacillus and other genera can also be used for production of zvegf4 proteins. Techniques for transforming these hosts and expressing foreign DNA sequences cloned therein are well known in the art (see, e.g., Sambrook et al., ibid.). When expressing a zvegf4 polypeptide in bacteria such as E. coli, the polypeptide may be retained in the cytoplasm, typically as insoluble granules, or may be directed to the periplasmic space by a bacterial secretion sequence. In the former case, the cells are lysed, and the granules are recovered and denatured using, for example, guanidine isothiocyanate or urea. The denatured polypeptide can then be refolded and dimerized by diluting the denaturant, such as by dialysis against a solution of urea and a combination of reduced and oxidized glutathione, followed by dialysis against a buffered saline solution. In the alternative, the protein may be recovered from the cytoplasm in soluble form and isolated without the use of denaturants. The protein is recovered from the cell as an aqueous extract in, for example, phosphate buffered saline. To capture the protein of interest, the extract is applied directly to a chromatographic medium, such as an immobilized antibody or heparin-Sepharose column. Secreted polypeptides can be recovered from the periplasmic space in a soluble and functional form by disrupting the cells (by, for example, sonication or osmotic shock) to release the contents of the periplasmic space and recovering the protein, thereby obviating the need for denaturation and refolding.
Transformed or transfected host cells are cultured according to conventional procedures in a culture medium containing nutrients and other components required for the growth of the chosen host cells. A variety of suitable media, including defined media and complex media, are known in the art and generally include a carbon source, a nitrogen source, essential amino acids, vitamins and minerals. Media may also contain such components as growth factors or serum, as required. The growth medium will generally select for cells containing the exogenously added DNA by, for example, drug selection or deficiency in an essential nutrient which is complemented by the selectable marker carried on the expression vector or co-transfected into the host cell.
Zvegf4 polypeptides or fragments thereof can also be prepared through chemical synthesis according to methods known in the art, including exclusive solid phase synthesis, partial solid phase methods, fragment condensation or classical solution synthesis. See, for example, Merrifield, J. Am. Chem. Soc. 85:2149, 1963; Stewart et al., Solid Phase Peptide Synthesis (2nd edition), Pierce Chemical Co., Rockford, Ill., 1984; Bayer and Rapp, Chem. Pept. Prot. 3:3, 1986; and Atherton et al., Solid Phase Peptide Synthesis: A Practical Approach, IRL Press, Oxford, 1989.
Covalent complexes can also be made by isolating the desired component polypeptides and combining them in vitro. Covalent complexes that can be prepared in this manner include homodimers of zvegf4 polypeptides, heterodimers of two different zvegf4 polypeptides, and heterodimers of a zvegf4 polypeptide and a polypeptide from another family member of the VEGF/PDGF family of proteins. The two polypeptides are mixed together under denaturing and reducing conditions, followed by renaturation of the proteins by removal of the denaturants. Removal can be done by, for example, dialysis or size exclusion chromatography to provide for buffer exchange. When combining two different polypeptides, the resulting renaturated proteins may form homodimers of the individual components as well as heterodimers of the two polypeptide components. See, Cao et al., J. Biol. Chem. 271:3154-3162, 1996.
Zvegf4 proteins are purified by conventional protein purification methods, typically by a combination of chromatographic techniques. See, in general, Affinity Chromatography: Principles and Methods, Pharmacia LKB Biotechnology, Uppsala, Sweden, 1988; and Scopes, Protein Purification: Principles and Practice, Springer-Verlag, New York, 1994. Proteins comprising a polyhistidine affinity tag (typically about 6 histidine residues) are purified by affinity chromatography on a nickel chelate resin. See, for example, Houchuli et al., Bio/Technol. 6: 1321-1325, 1988. Proteins comprising a glu-glu tag can be purified by immunoaffinity chromatography according to conventional procedures. See, for example, Grussenmeyer et al., ibid. Maltose binding protein fusions are purified on an amylose column according to methods known in the art.
Zvegf4 proteins can be used wherever it is desired to stimulate the production of bone and/or connective tissue in both humans and non-human animals. Veterinary uses include use in domestic animals, including livestock and companion animals. Specific applications include, without limitation, fractures, including non-union fractures and fractures in patients with compromised healing, such as diabetics, alcoholics, and the aged; bone grafts; healing bone following radiation-induced osteonecrosis; implants, including joint replacements and dental implants; repair of bony defects arising from surgery, such as cranio-maxilofacial repair following tumor removal, surgical reconstruction following tramatic injury, repair of hereditary or other physical abnormalities, and promotion of bone healing in plastic surgery; treatment of periodontal disease and repair of other dental defects; treatment of bone defects following therapeutic treatment of bone cancers; increase in bone formation during distraction osteogenesis; treatment of joint injuries, including repair of cartilage and ligament; repair of joints that have been afflicted with osteoarthritis; tendon repair and re-attachment; treatment of osteoporosis (including age-related osteoporosis, post-menopausal osteoporosis, glutocorticoid-induced osteoporosis, and disuse osteoporosis) and and other conditions characterized by increased bone loss or decreased bone formation;, elevation of peak bone mass in pre-menopausal women; and use in the healing of connective tissues associated with dura mater.
For use within the present invention, zvegf4 proteins are formulated for local or systemic (particularly intravenous or subcutaneous) delivery according to conventional methods. In general, pharmaceutical formulations will include a zvegf4 protein in combination with a pharmaceutically acceptable delivery vehicle. Delivery vehicles include biocompatible solid or semi-solid matrices, including powdered bone, ceramics, biodegradable and non-biodegradable synthetic polymers, and natural polymers; tissue adhesives (e.g., fibrin-based); aqueous polymeric gels; aqueous solutions; liposomes; and the like. Exemplary formulations and delivery vehicles are disclosed below. This disclosure is illustrative; those skilled in the art will readily recognize suitable alternatives, including derivatives of the specifically named materials and combinations of materials. Formulations may further include one or more additional growth factors, excipients, preservatives, solubilizers, buffering agents, albumin to prevent protein loss on vial surfaces, etc. Methods of formulation are well known in the art and are disclosed, for example, in Remington: The Science and Practice of Pharmacy, Gennaro, ed., Mack Publishing Co., Easton, Pa., 19th ed., 1995. An xe2x80x9ceffective amountxe2x80x9d of a composition is that amount that produces a statistically significant effect, such as a statistically significant increase in the rate of fracture repair, reversal of bone loss in osteoporosis, increase in the rate of healing of a joint injury, increase in the reversal of cartilage defects, increase or acceleration of bone growth into prosthetic devices, improved repair of dental defects, and the like. The exact dose will be determined by the clinician according to accepted standards, taking into account the nature and severity of the condition to be treated, patient traits, etc. Determination of dose is within the level of ordinary skill in the art. Depending upon the route and method of administration, the protein may be administered in a single dose, as a prolonged infusion, or intermittently over an extended period. Intravenous administration will be by bolus injection or infusion over a typical period of one to several hours. Sustained release formulations can be employed. In general, a therapeutically effective amount of zvegf4 is an amount sufficient to produce a clinically significant change in the treated condition, such as a clinically significant reduction in time required for fracture repair, a significant reduction in the volume of a void or other defect, a significant increase in bone density, a significant reduction in morbidity, or a significantly increased histological score.
Zvegf4 will ordinarily be used in a concentration of about 10 to 100 xcexcg/ml of total volume, although concentrations in the range of 1 ng/ml to 1000 xcexcg/ml may be used. For local application, such as for the regeneration of bone in a fracture or other bony defect, the protein will be applied in the range of 0.1-100 xcexcg/cm2 of wound area.
Within the present invention zvegf4 can be used in combination with other growth factors and other therapeutic agents that have a positive effect on the growth of bone or connective tissue. Such growth factors include insulin-like growth factor 1 (IGF-1), PDGF, alpha and beta transforming growth factors (TGF-xcex1 and TGF-xcex2), epidermal growth factor (EGF), bone morphogenetic proteins, leukemia inhibitory factor, and fibroblast growth factors. Other therapeutic agents include vitamin D, bisphosphonates, calcitonin, estrogens, parathyroid hormone, osteogenin, NaF, osteoprotegerin, and statins.
Zvegf4 can be delivered as a component of a tissue adhesive. Fibrin-based tissue adhesives are known in the art, and can be prepared from plasma or recombinant sources. Tissue adhesives comprise fibrinogen and factor XIII to which thrombin is added immediately before use to activate cross-linking. See, for example, Schwarz et al., U.S. Pat. No. 4,414,976; Stroetmann et al., U.S. Pat. No. 4,427,650; and Rose et al., U.S. Pat. No. 4,928,603. The use of tissue adhesives may be particularly advantageous in the treatment of conditions where connective tissue must be repaired, such as torn ligaments or tendons.
Solid and semisolid matrices are preferred delivery vehicles for filling non-union fractures, cavities, and other bony defects. These matrices provide a space-filling substitute for the natural bone, and include bone substituting agents such as tricalcium phosphate, hydroxyapatite, combinations of tricalcium phosphate and hydroxyapatite, polymethylmethacrylate, aluminates and other ceramics, and demineralized freeze-dried cortical bone. Solid and semi-solid matrices can also be prepared from a variety of polymeric materials. Semi-solid matrices provide the advantage of maleability such that they can be shaped to provide a precise filling of a bony defect. Matrices may include other active or inert components. Of particular interest are those agents that promote tissue growth or infiltration. Agents that promote bone growth include bone morphogenic proteins (U.S. Pat. No. 4,761,471; PCT Publication WO 90/11366), osteogenin (Sampath et al., Proc. Natl. Acad. Sci. USA 84: 7109-7113, 1987), and NaF (Tencer et al., J. Biomed. Mat. Res. 23: 571-589, 1989).
Biodegradable, synthetic polymers include polyesters, polyorthoesters, polyanhydrides, polycarbonates, polyfumarates, polyhydroxybutyrate, vinyl polymers, and the like. Specific examples include, without limitation, polylactide, polyglycolide, polylactide/polyglycolide copolymers, polydioxanone, polyglycolide/trimethylene carbonate copolymers, polyacrylic acid, polymethacrylic acid, polyvinyl pyrrolidone, and polyvinyl alcohol. Such materials can be prepared in a variety shapes, including films, plates, pins, rods, screws, blocks, lattices, and the like for attachment to or insertion into bone. See, for example, Walter et al., U.S. Pat. No. 5,863,297; and WIPO publication WO 93/20859. These materials may further include a carrier such as albumin, a polyoxyethylenesorbitan detergent or glutamic acid. In principle, any substance that enhances polymer degradation, creates pores in the matrix or reduces adsorption of the growth factor(s) to the matrix can be used as a carrier. Polyoxyethylenesorbitan detergents that are useful as carriers include polyoxyethylenesorbitan monooleate, polyoxyethylenesorbitan monolaureate, polyoxyethylenesorbitan monopalmitate, polyoxy-ethylenesorbitan monostearate and polyoxyethylenesorbitan trioleate. Plasticizers can also be included.
In general, a film or device as described herein is applied to the bone at a site of injury. Application is generally by implantation into the bone or attachment to the surface using standard surgical procedures.
Biodegradable polymer films are particularly useful as coatings for prosthetic devices and surgical implants. Such films can, for example, be wrapped around the outer surfaces of surgical screws, rods, pins, plates and the like, or can themselves be rolled or otherwise formed into a variety of shapes. Implantable devices of this type are routinely used in orthopedic surgery. Films can also be used to coat bone filling materials, such as hydroxyapatite blocks, demineralized bone matrix plugs, collagen matrices, and the like.
As used herein the term xe2x80x9ccopolymerxe2x80x9d includes any polymer containing two or more types of monomer unit. Copolymers can be classified in four types as shown in the following chart, wherein xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d denote the component monomer units:
Degradation of the matrix and consequent release of growth factors therefrom can be modulated by adjusting such parameters as molecular weight, copolymer structure, copolymer ratio, matrix thickness, and porosity, and by including a carrier as disclosed above. PLA/PGA films, for example, are generally formulated to provide a ratio of PLA:PGA between 75:25 and 25:75, more commonly between 65:35 and 35:65. In general, an implant will be prepared using a copolymer having a molecular weight between 10,000 and 200,000 Daltons. In general, lower molecular weight copolymers will degrade more rapidly than higher molecular weight formulations; random copolymers are less crystalline and therefore degrade more quickly than other types of copolymers; and polymers of enantiomeric lactides are crystalline and therefore more resistant to degradation than their racemic counterparts.
Polymer matrices are prepared according to procedures known in the art. See, for example, Loomis et al., U.S. Pat. No. 4,902,515; Gilding and Reed, Polymer 20: 1459-1464, 1979; and Boswell et al., U.S. Pat. No. 3,773,919. For example, PLA/PGA copolymer implants are produced by combining the desired amount of PLA/PGA copolymer granules in a suitable solvent (e.g., chloroform or methylene chloride), pouring the resulting solution into a mold, and completely evaporating the solvent. In the alternative, PLA/PGA implants can be produced by compression molding, extrusion, or other known methods. To load the matrix, zvegf4 and a carrier are applied as powders or liquid solutions. For example, lyophilized zvegf4 and albumin may be uniformly dispersed over one surface of polymer film, and the film folded over. By repeated this process, a multi-layered xe2x80x9csandwichxe2x80x9d of polymer and growth factor can be constructed. In the alternative, the proteins can be applied as aqueous solutions (e.g., in phosphate buffered saline or 0.1 M acetic acid), which are allowed to dry. Porous implants can be soaked in a solution of zvegf4 (optionally containing other components), and the liquid evaporated. Zvegf4 can be worked into a maleable polymeric matrix after which the matrix is formed into the desired shape and cured at elevated temperature (e.g., 60-65xc2x0 C.). Porous implants can be prepared by curing the matrix under vacuum.
Zvegf4 can also be delivered in combination with a biodegradable sponge, for example a gelatin, collagen, cellulose, or chitin sponge. Such sponges are known in the art. See, for example, Correll, U.S. Pat. No. 2,465,357; Miyata et al., U.S. Pat. No. 4,271,070; and Munck et al., WO 90/13320. A solution of zvegf4 and, optionally, one or more additional therapeutic agents is injected into the sponge, and the sponge is air-dried at a temperature of 30-100xc2x0 C. for a time sufficient to reduce the water content to below 50%, preferably below 10%.
Gels can also be used as delivery vehicles. The use of aqueous, polymeric gels for the delivery of growth factors is disclosed by, for example, Finkenaur et al., U.S. Pat. No. 5,427,778; Edwards et al., U.S. Pat. No. 5,770,228; and Finkenaur et al., U.S. Pat. No. 4,717,717; and Cini et al., U.S. Pat. No. 5,457,093. Gels comprise biocompatible, water soluble or water swellable polymers that form viscous solutions in water. Such polymers include, without limitation, polysaccharides, including methyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, hydroxyethyl cellulose, dextrans, starch, chitosan, and alginic acid; glycosaminoglycans, including hyaluronic acid, chondroitin, chondroitin sulfates, heparin, and heparan sulfate; proteins, including collagen, gelatin, and fibronectin; and acrylamides, including polyacrylamide and polymethacrylamide. Gels are generally prepared with a viscosity of from 200 cps to 100,000 cps, more commonly about 1000 cps to 30,000 cps at room temperature, the latter range corresponding to about 0.25-10% hydroxyethyl cellulose in water. Higher viscosity gels are known in the art (e.g., Finkenaur et al., U.S. Pat. No. 5,427,778). Viscosity can be adjusted by varying the concentration and/or length of the component polymer(s). Gels are prepared by combining the polymer with a suitable buffer, such as a low ionic strength citrate, phosphate, or acetate buffer at neutral or slightly acidic pH. A preservative (antimicrobial agent) such as methyl paraben, propyl paraben, benzyl alcohol, or the like, will generally be included. Following thorough mixing, the solution is sterilized by suitable means (e.g., autoclaving). The mixture is cooled, and filter-sterilized zvegf4 is added.
Alternative means for local delivery of zvegf4 include osmotic minipumps (e.g., ALZET(copyright) minipumps; Alza Corporation, Mountain View, Calif.); electrically charged dextran beads as disclosed in Bao et al. (WO 92/03125); collagen-based delivery systems, such as disclosed in Ksander et al. (Ann. Surg. 211:288-294, 1990); and alginate-based systems as disclosed in Edelman et al. (Biomaterials, 12:619-626, 1991). Other methods known in the art for sustained local delivery in bone include porous coated metal protheses that can be impregnated with a therapeutic agent and solid plastic rods with therapeutic compositions incorporated within them.
Zvegf4 can be further used to treat osteoporosis by administering a therapeutically effective amount of zvegf4 to an individual. Zvegf4 proteins can be further tested in known animal models using an in vivo dosing assay. Prototypical dosing may be accomplished by subcutaneous, intraperitoneal or oral administration, and may be performed by injection, sustained release or other delivery techniques. The time period for administration of avegf4 may vary (for instance, 28 days as well as 35 days may be appropriate).
Delivery of systemically adminstered compositions of the present invention may be enhanced by conjugating zvegf4 to a targeting molecule. A xe2x80x9ctargeting moleculexe2x80x9d is a molecule that binds to the tissue of interest. For example, bone-targeting molecules include tetracyclines, calcein, bisphosphonates, polyaspartic acid, polyglutamic acid, aminophosphosugars, peptides known to be associated with the mineral phase of bone (e.g., osteonectin, bone sialoprotein, and osteopontin), bone-specific antibodies, proteins with bone mineral or bone cell binding domains (e.g., calcitonin), and the like. See, for example, the disclosures of Bentz et al., EP 512,844; Murakami et al., EP 341,961; and Brinkley, Bioconjugate Chem. 3:2-13, 1992. Conjugation will ordinarily be achieved through a covalent linkage, the precise nature of which will be determined by the targetting molecule and the linking site on the zvegf4 polypeptide. Typically, a non-peptidic agent is modified by the addition of a linker that allows conjugation to zvegf4 through its amino acid side chains, carbohydrate chains, or reactive groups introduced on zvegf4 by chemical modification. For example, a drug may be attached through the xcex3-amino group of a lysine residue, through a free et-amino group, by disulfide exchange to a cysteine residue, or by oxidation of the 1,2-diols in a carbohydrate chain with periodic acid to allow attachment of drugs containing various nucleophiles through a Schiff-base linkage. See, for example, Ali et al., U.S. Pat. No. 4,256,833. Protein modifying agents include amine-reactive reagents (e.g., reactive esters, isothiocyantates, aldehydes, and sulfonyl halides), thiol-reactive reagents (e.g., haloacetyl derivatives and maleimides), and carboxylic acid- and aldehyde-reactive reagents. Zvegf4 polypeptides can be covalently joined to peptidic agents through the use of bifunctional cross-linking reagents. Heterobifunctional reagents are more commonly used and permit the controlled coupling of two different proteins through the use of two different reactive moieties (e.g., amine-reactive plus thiol, iodoacetamide, or maleimide). The use of such linking agents is well known in the art. See, for example, Brinkley (ibid.) and Rodwell et al., U.S. Pat. No. 4,671,958. Peptidic linkers can also be employed. In the alternative, a zvegf4 polypeptide can be linked to a peptidic moiety through preparation of a fusion polypeptide.
Zvegf4 can be implanted in a mammalian body so that the zvegf4 is in contact with osteoblasts such that osteoblast proliferation occurs and bone growth is stimulated. For example, zvegf4 can be placed in a matrix in association with a bone morphogenic protein (BMP). The BMP induces the migration of mesenchymal osteoblast precursors to the site and further induces differentiation of the mesenchymal cells into osteoblasts. Zvegf4 will then stimulate the further proliferation of the osteoblasts. A suitable matrix is made up of particles of porous materials. The pores must be of a dimension to permit progenitor cell migration and subsequent differentiation and proliferation, generally in the range of 70-850 xcexcm, commonly from 150 xcexcm to 420 xcexcm. The matrix containing the zvegf4 can be molded into a shape encompassing a bone defect. Examples of matrix materials are particulate, demineralized, guanidine extracted, species-specific bone. Other potentially useful matrix materials include collagen, homopolymers and copolymers of glycolic acid and lactic acid, hydroxyapatite, tricalcium phosphate and other calcium phosphates. Zvegf4 can be applied into a matrix at a sufficient concentration to promote the proliferation of osteoblasts, preferably at a concentration of at least 1 xcexcg/ml of matrix. A solution of zvegf4 can also be injected directly into the site of a bone fracture to expedite healing of the fracture. Examples of BMPs and the use of matrices to produce are disclosed in PCT application publication number WO 92/07073, publication No. WO 91/05802, U.S Pat. No. 5,645,591 and U.S. Pat. No. 5,108,753.
As stated above, zvegf4 may also be used to promote the production of cartilage through its ability to stimulate the development or proliferation of chondrocytes. Zvegf4 can be injected directly into the site where cartilage is to be grown. For example, zvegf4 can be injected directly in joints which have been afflicted with osteoarthritis or other injured joints in which the cartilage has been worn down or damaged by trauma. In the alternative, zvegf4 can be deliverd in a suitable solid or semi-solid matrix as disclosed above.
Cartilage can also be grown by first removing chondrocytes from a patient and culturing them in the presence of zvegf4 so that they proliferate. Chondrocytes are cultured for from several hours to a day or longer according to conventional methods in a culture medium (e.g., DMEM supplemented with 10% patient""s serum) containing from about 0.1 xcexcg/ml to about 100 xcexcg/ml zvegf4. The proliferated chondrocytes are reimplanted into the patient where cartilage needs to be produced. The proliferated chondrocytes can be delivered in a porous matrix having sufficient porosity to permit cell ingrowth as generally disclosed above. Additional zvegf4 can be included in the matrix to promote further chondrocyte proliferation after implantation. See, in general, Walter et al., U.S. Pat. No. 5,863,297 and Boyan et al., U.S. Pat. No. 6,001,352.
Within another embodiment, the present invention provides methods for stimulating the growth and/or differentiation of bone-forming and cartilage-forming cells, or their precursors, in vitro. Using these methods, cells can be harvested from a patient, expanded ex vivo, and returned to the patient as generally disclosed above. Of particular interest is the growth and/or differentiation of bone marrow cells, which can be cultured in the presence of differentiation-stimulating agents to develop into, inter alia, osteoblasts, osteoclasts, and chondrocytes. Identification of differentiated cells within a primary culture is primarily phenotypic. For example, the phenotypic markers for osteoblasts include expression of alkaline phosphatase (Manduca et al., J. Bone Min. Res. 8:281, 1993), type 1 collagen synthesis (Kurihara et al., Endocrinol. 118(3):940-947, 1986), production of osteocalcin (Yoon et al., Biochem. 27:8521-8526, 1988) and responsiveness to parathyroid hormone (Aubin et al., J. Cell Biol., 92:452-461, 1982). Osteoblast cells are typically cultured at 37xc2x0 C. in 5% CO2 in a growth medium that includes a carbon source, a nitrogen source, essential amino acids, vitamins, minerals and growth factors generally supplied by fetal calf serum. A variety of suitable media are known in the art. Zvegf4 polypeptides are added to tissue culture media for these cell types at a concentration of about 10 pg/ml to about 1000 ng/ml. Those skilled in the art will recognize that zvegf4 proteins can be advantageously combined with other growth factors in culture media.
Bony defects or connective tissue injuries may also be repaired using a gene therapy approach wherein a polynucleotide encoding zvegf4 is administered to a patient. Gene delivery systems useful in this regard include adenovirus, adeno-associated virus, and naked DNA vectors. See, for example, by Anderson et al., U.S. Pat. No. 5,399,346; Mann et al., Cell 33:153, 1983; Temin et al., U.S. Pat. No. 4,650,764; Temin et al., U.S. Pat. No. 4,980,289; Markowitz et al., J. Virol. 62:1120, 1988; Temin et al., U.S. Pat. No. 5,124,263; Dougherty et al., WIPO publication WO 95/07358; and Kuo et al., Blood 82:845, 1993. Of particular interest is local infection of the affected tissue, such as local application of the vector to a periodontal pocket, fracture, joint, implant site, or site of prosthetic attachment.